Re: Dish at 90 deg to 4m yagi

Phil Boorman G0JBA


The bottom lower edge of the dish.

On Thursday, October 20, 2016, 13:06, Conrad PA5Y g0ruz@... [ukmicrowaves] wrote:


Do you mean that the lower edge of the dish is 1.4m above the 4m antenna Phil or the central mounting point.


Conrad PA5Y

On 20 October 2016 09:05:27 CEST, "Phil Boorman g0jba@... [ukmicrowaves]" wrote:

I used a 1.2m Swedish Mircowave Dish  (13cm band) mounted 1.4m above a 7ele 4m Yagi and couldn't detect any noticeable differences on transmit or receive.   As you say 'it's 4m' and a band that is variable at best.  23cm is much more serious.

Phil G0JBA

On Wednesday, October 19, 2016, 22:56, Conrad PA5Y g0ruz@... [ukmicrowaves] wrote:


Hello Chris OK on the windload, the mast and rotator can handle the forces head on to the wind at 160kph, there is data on the RFHAMDESIGN site for the dish that agrees closely with an old graph that I have from JPL.

I was also (mainly) considering the effects on the 4m antenna from a performance perspective. I will put the 4m antenna 1/2 stacking distance above the dish, I think that will be the best until I get a 3rd tropo mast. I thought perhaps that having the dish orthogonal to the plane of the yagi elements would be better.

Anyway I'm only messing about in the UKAC on 4m, 23cms is an altogether more serious matter.


Conrad PA5Y

On 19/10/2016 20:51, Christopher Bartram cbartram@... [ukmicrowaves] wrote:
Hello Conrad

What no one has any experience or comments on this?

I find that surprising.

It has been over 6 hrs since I posted ;-)

I suspect that's because few people in the use dishes on 1.3GHz nowadays. That's a pity ... I'm still considering the use of a dish for tropo. from here, basing my thoughts on the very good results I had in the late '80's from IO70 on 1.3GHz.

I know little structural engineering, but I'm not altogether sure that parking the dish at right-angles to the wind would give as great a gain wrt. stresses as you might think. A deep mesh dish, eg. f/D =  0.3 or 0.4, will still project quite a significant profile, even edge-on, which will, in effect have around twice the effect of a an equivalent planar structure.

My old tropo dish along with a HB 6m yagi went through the Great Storm of 1987 sat on top of a Telomast - which was guyed - above an old AR40 rotator. It survived without a problem, despite being parked not so far from a right angle to the wind. The survival of the rotator was the greatest miracle in my direct experience that night!

Vy 73



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